This invention is generally directed to improvements in acoustic surface wave devices. It is particularly directed to an acoustic surface wave filter for multiplexing a pair of signal inputs to develop a filtered signal output.
Exemplary surface wave filters of the type considered herein are designed to receive and filter one of two possible input signals. For example, a filter may have one input port adapted to receive a signal corresponding to channel 3 of the television spectrum, another input port adapted to receive a signal corresponding to channel 4 of the television spectrum, and a single output port. Thus, the device is adapted to receive either of two input signals and to develop therefrom an output signal from which spurious components have been removed by filtering.
Design objectives of such filters include minimizing the size of the filter's substrate, eliminating the effects of acoustic reflections from substrate edges, and minimizing the filter's insertion loss. To some extent, these objectives are met in prior designs, such as that described in U.S. application, Ser. No. 290,649, filed Aug. 7, 1981, and now U.S. Pat. No. 4,379,274, the pertinent teachings of which are included herein by reference. Nevertheless, fabrication costs require further reduction in substrate size without sacrificing performance characteristics.
Accordingly, it is a general object of the invention to provide an improved multiplexing filter constructed as an acoustic surface wave device.
It is a more specific object of the invention to provide such a filter which employs a relatively small substrate without compromising filter performance.